This application points out the usefulness of the acellular slime mold Physarum polycephalum as a model system for biochemical, genetic, ultrastructural, and phenomenological studies of the molecular bases of a wide variety of eukaryotic cell movements. Biochemical studies of plasmodial actin and myosin will continue as well as attempts to identify and characterize other proteins which might function in vivo to organize and/or regulate actin or myosin. These studies will not only provide a more detailed understanding of the molecular events involved in protoplasmic streaming, but, in conjunction with comparative studies on microplasmodia and on the amoeboid gametes, will also provide a basis for the use of mutants to show that particular biochemical activities are involved in specific motility processes. Techniques based on the use of columns of glass beeds will be employed to select mutants with temperature-sensitive defects in amoebal movements and in the processes occurring during the amoebo-flagellate transformation. Phenomenological and ultrastructural studies of amoebal cell movements and of their synchronous transformation into elongate flagellate swimmers will focus on the roles of microtubular and microfilamentous elements in various motility phenomena and will also provide valuable information with which to determine the particular defect in specific mutants. Tubulin and dynein will be isolated from flagellate swimmers and their roles and/or fates viz a viz those of actin and myosin, in the complex of events involved in the transformation will be defined. The development of several in vitro motility models may aid in evaluating specific hypotheses as to the molecular nature of motility causation and control.